When polyvinyl acetate is combined with active ingredients to form encapsulation mixtures or gradual release structures for use in chewing gum, the ingredients are conventionally mixed using an extruder, such as a Leistritz or Werner-Pfleiderer single screw or twin screw extruder. Initially, the granular polyvinyl acetate and active ingredient are added to the extruder and heated to a temperature of about 90.degree. C. to about 110.degree. C., causing the polyvinyl acetate to melt and flow freely. The active ingredient may be a flavor ingredient, a flavor enhancing ingredient, a high intensity sweetener, or otherwise. The active ingredient is caused to mix with the polyvinyl acetate as the screws of the extruder turn and convey. The mixture is then extruded through a die, such as a slot die, to form a sheet-like extrudate. The extrudate is cooled to a solid form before being melt spun (in the case of gradual release structures) and/or ground into powder.
The initial cooling of the encapsulation mixture or gradual release structure is conventionally accomplished using an air venturi. The air venturi is an apparatus which simply aspires upon the extrudate and uses the force of air to blow it into a cooling trough. Once in the cooling trough, the extrudate is further cooled in air.
The polyvinyl acetate has a high heat capacity and heat retention, and low thermal conductivity. Accordingly, some of the polyvinyl acetate tends to remain in the molten state long after the encapsulation mixture or gradual release structure leaves the extruder. The air venturi is particularly ineffective in cooling the polyvinyl acetate which is located away from the surface, and near the core, of the extrudate. This prolonged heat history can cause undesirable degradation of the active ingredient which is being encapsulated in the polyvinyl acetate.
Active ingredients which are particularly susceptible to degradation due to prolonged heat exposure include but are not limited to sweeteners, flavors, flavor enhancers, and high intensity sweeteners such as Magnasweet. Degradation of active ingredient results in loss of activity, whether it be flavor, flavor enhancing or sweetening effect. Degradation is evidenced by an undesirable brown discoloration of the extrudate, which is normally white in appearance.
French Patent No. 2,503,989 discloses a cooling tunnel for cooling a raw extruded product, notably chewing gum. After exiting the extrusion head, the rectilinear material is conveyed in the as-extruded state by a conveyor belt along a cooling tunnel. The cooling is accomplished by evacuating the air from the internal space of the tunnel and feeding air cooled by the evaporation system of a cooling circuit.
European Patent Application No. 0,191,980 discloses the cooling of chewing gum slabs by placing the gum slabs on a metal conveyor belt which is cooled from underneath. The reference also discloses the blowing of cool air onto the surface of the gum slabs using fans.
U.S. Pat. No. 2,224,430 discloses passing a chewing gum mass between a pair of cooperating rollers disposed so as to provide a forming space therebetween for forming the gum into sticks. The peripheral walls of the rollers are cooled using a refrigerant, in order to prevent the chewing gum from sticking to the rollers, and to cause solidification of the chewing gum.
There is a need in the chewing gum industry for a cooling method which significantly increases the rates of cooling for encapsulation mixtures and gradual release structures which utilize polyvinyl acetate as the encapsulant or wall material, thereby reducing the degradation of heat sensitive active ingredients contained therein.